Liquid lubricants are well known and such lubricants have been, and are now, successfully used for many diverse purposes. Liquid lubricants have not, however, proved to be satisfactory for some uses, including, for example, use in high temperature environments where combustion or pyrolysis of conventional liquid lubricants would occur, at extremely low temperatures where conventional liquid lubricants would freeze or gel, and/or in highly oxidizing environments where conventional liquid lubricants would present an explosion hazard.
For such uses, the powders of crystalline solids have long been used as lubricants, and, more specifically, powdered graphite has long been used in industry as a lubricant for use in hostile environments in which oils and greases are forbidden.
In its natural state, graphite absorbs moisture from the atmosphere and this moisture is essential to the graphite functioning as a lubricant. If graphite is exposed to a vacuum for extended periods however, the moisture is lost and the graphite becomes abrasive. To overcome this problem, graphite lubricating compositions, including iodine and other moisture substitutes, have heretofore been developed for specific applications.
Molybdenum disulfide (MoS.sub.2), a natural material, has properties similar to those of graphite but does not require moisture for good lubricating performance. For this reason, molybdenum disulfide has more recently been used in the aerospace industry as a lubricant for satellites and space vehicles and in other areas where oils and greases are forbidden or difficult to employ, such as, for example, in self-lubricating bearings and food processing machinery. In addition, molybdenum disulfide has also been utilized as an additive to oils and greases to improve their performance at extremely high loads.
In attempting to improve the lubricating effectiveness of solid lubricants for space applications, it was empirically found that mixtures of silver, antimony oxide and molybdenum disulfide exhibited superior lubricating performance to molybdenum disulfide alone. Subsequently, it was found that other metal disulfides and diselenides, including tungsten disulfide (WS.sub.2), molybdenum diselenide (MoSe.sub.2), and tungsten diselenide (WSe.sub.2) are good solid lubricants.
These materials are usually found in the form of powders, however, which are difficult to use as lubricants for at least some applications, including, for example, rolling bearings and mechanical components such as gears. Therefore, these powders are normally used in combination with binders which bond them to surfaces or are used in combination with a structural material to form self-lubricating solids.
While solid lubricants have heretofore been suggested and/or utilized, particularly where liquid lubricants could not be satisfactorily utilized, such solid lubricants have nevertheless not been found to be satisfactory, at least for some applications, and better solid lubricating compositions have therefore still been needed.